"If you were president, what would you do about Syria and the humanitarian crisis in Aleppo?" Raddatz asked, reading a question submitted online. "Isn't it a lot like the Holocaust when the US waited too long before we helped?"

Clinton answered first, and then Trump started his response by attacking her.

"First of all, she was there, as secretary of state, with the so-called line in the sand," Trump said, referring to the "red line" President Barack Obama drew, and then backed away from, on chemical weapons in Syria.

Clinton cut in to say that she was not secretary of state at the time.

"You were in total contact with the White House," Trump said. "And, perhaps, sadly, Obama probably still listened to you. I don't think he'll be listening to you very much anymore."

He continued: "Obama draws the line in the sand. It was laughed at all over the world what happened."

Trump then pivoted to Russia.

"Now, with that being said, she talks tough against Russia, but our nuclear program has fallen way behind and they've gone wild with their nuclear program," he said. "Not good."

The Republican nominee then pivoted back to Syria.

"She talks in favor of the rebels. She doesn't even know who the rebels are," Trump said. "You know, every time we take rebels, whether it's in Iraq or anywhere else, we're arming people. And you know what happens? They end up being worse than the people."

Trump cited Libya as an example.

He then went back to talking about Russia, eventually going back to Syria at the end of his two-minute time period.

"One thing I have to say — I don't like [Syrian President Bashar] Assad at all, but Assad is killing ISIS," Trump said. "Russia is killing ISIS. And Iran is killing ISIS. And those three have now lined up because of our weak foreign policy."

Trump's answer apparently wasn't satisfactory to Raddatz.

"Mr. Trump, let me repeat the question," she said. "If you were president, what would you do about Syria and the humanitarian crisis in Aleppo?"

She then recalled a recent statement from Trump's running mate, Indiana Gov. Mike Pence, who said, "Provocations by Russia need to be met with American strength and that if Russia continues to be involved in airstrikes along with the Syrian government forces of Assad, the United States of America should be prepared to use military force to strike the military targets of the Assad regime."

Trump said he disagreed with Pence on this issue.

"He and I haven't spoken and I disagree," Trump said. "I think we have to knock out ISIS. Right now, Syria is fighting ISIS. We have people that want to fight both at the same time. But Syria is no longer Syria. Syria is Russia. And it's Iran, who she made strong. ... I believe we have to get ISIS. We have to worry about ISIS before we can get too much more involved."

He then went back to the red line.

"She had a chance to do something with Syria, they had a chance," Trump said. "And that was the line."